1. Field of the Invention
The present invention relates to an expectorant and a method of removing sputum by using the expectorant. More particularly, the invention is concerned with an expectorant made of N-acetylneuraminic acid and its pharmaceutically active salt having an effect of directly promoting ciliary motion while acting on the rheological property of sputum, as well as to a method of removing sputum by such an expectorant.
2. Description of the Related Art Including Information
Viscous secretion exists in the airway of the human body. The secretion has an important role in imparting suitable temperature and humidity to inhaled air. The matter generally referred to as "sputum" is constituted mainly by this secretion.
When its amount is moderate, the secretion in the airay, is unconsciously swallowed or expelled with the breath, but usually is never expectorated. Thus, any expectoration suggests that there is something extraordinary in the respiratory system. On the other hand, accumulation of spatum to be expectorated in the airway is liable to cause an infection via the airway. From this point of view, the removal of sputum is a matter of great significance in the medical treatment of patients who suffer with a disease in the airway.
Sputum is often very viscous and sticky so that expectoration causes the patient pain. In order to facilitate expectoration, therefore, medicine which is referred to as "expectorant" has been used. This medicine is given in a general dosage orally or by injection. The expectorant thus dosed serves to remove sputum by diluting the sputum through an increase in secretion by the mucosa of the airway, promotion of separation from the mucosa and enhancement of ciliary beat. General dosages, however, involve various clinical problems concerning mechanism and effect.
The present inventors have therefore made intensive studies and found that sialic acids can be used as a compound which is an effective expectorant which can be used in local dosages. This invention has been accomplished through a study on the sputum removing effect offered by N-acetylneuraminic acid and its salt, among the sialic acids.